1. Field of the Invention
The present invention relates generally to methods and tools for deploying a device through a barrier. More particularly, the present invention relates to methods and tools for deploying spinous process constraint devices through tissue in patients having back pain or other spinal conditions.
The human spine structure includes four curves that generally form an “S” shape. One of these curves, lumbar lordosis, results in an intervertebral space that is larger in the front (anterior) than back (posterior). Unfortunately, a backward shift in the intervertebral disc in this lower back region is particularly susceptible to pain generation since the nerve roots and dura matter emerge at the posterior aspect of the vertebral column. The evolutional change to an upright position has not included concomitant anatomical adaption. Thus, the human spine has an anatomy that more readily withstands extension (i.e. standing or arching backwards) rather than flexion (i.e. sitting or bending forward) and can quickly destabilize during certain movements.
Spinal stability is highly dependent on the patency of attached soft tissue such as ligaments, spinal load and posture as well as task requirements. In particular, the ligaments and disc play a key role in keeping each spine segment stable and aligned. Degeneration of ligaments, disc or other tissue structures can lead to inability of the spine segment to maintain stability even over a normal range of loads. Instability of the lumbar spine has been suggested to be both a cause and a consequence of acute, recurring or chronic low back pain. It is estimated that 80% of the general population will suffer from backache or lumbago during their lifetime (Fryomoyer et al., “An Overview of the Incidence and Costs of Low Back Pain” Orthrop. Clin. North Am. (1991) 22:263-271).
A major source of chronic low back pain is discogenic pain, also known as internal disc disruption. Patients suffering from discogenic pain tend to be young, otherwise healthy individuals who present with pain localized to the back. Discogenic pain usually occurs in the lower back at the discs located at the L4-L5 or L5-S1 junctions of the lumbar spine. Pain tends to be exacerbated when patients put their spines into flexion and relieved when they put their lumbar spines into extension. Flexion and extension are known to change the mechanical loading pattern of a lumbar segment. During extension, the axial loads borne by this segment are shared by the disc and the facet joints. It is estimated that about 30% of the load is borne by the facet joints. In flexion, however, the segmental load is borne almost entirely by the disc. Furthermore, when the segment is in flexion, the nucleus shifts posteriorly, changing the loads on the posterior portion of the annulus (which is innervated), likely causing its fibers to be subject to tension and shear forces. Segmental flexion, then, both increases the loads borne by the disc and causes them to be borne in a more painful way. Discogenic pain can be severely disabling. For some patients, it can deleteriously affect their ability to work, recreate and otherwise enjoy their lives.
Pain experienced by patients with discogenic low back pain can be thought of as flexion instability, and is related to flexion instability manifested in other conditions. The most prevalent of these is spondylolisthesis, a spinal condition in which abnormal segmental translation is exacerbated by segmental flexion. This condition is characterized by a forward slipping (i.e. anterior displacement) of one or more vertebrae that invariably results in stenosis of the spinal canal. Slippage can occur if the adjacent ligatures are weak, which is often the case in the lumbar area, particularly if people live a sedentary life style. The tools described herein may be used to help deploy spinal implants that treat these and other spinal disorders associated with segmental flexion for which the prevention or control of spinal segmental flexion is desired.
Patients with discogenic pain accommodate their syndrome by avoiding positions such as sitting, which cause their painful segment to go into flexion, and preferring positions such as standing, which maintain their painful segment in extension. One approach to reducing discogenic pain involves the use of a lumbar support often seen in office chairs. Biomechanically, the attempted effect of the ubiquitous lumbar support is also to maintain the painful lumbar segment in the less painful extension position.
Current treatment alternatives for patients diagnosed with back pain are limited. At one end of the treatment continuum, a patient may elect to follow a conservative path, such as physical therapy, massage, anti-inflammatory and analgesic medications, muscle relaxants, and/or epidural steroid injections. This is usually the first treatment option because it is simple and least invasive. However, most of these patients continue to suffer with a significant degree of pain.
At the opposite end of the treatment spectrum, a patient may elect to undergo invasive and risky surgeries including spinal fusion. Fusion often requires discectomy (i.e. removal of the disk) together with fusion of adjacent vertebra. This procedure may or may not also include instrumentation of the affected spinal segment including, for example, pedicle screws and stabilization rods. Fusion is not usually recommended for discogenic pain because it is irreversible, costly, associated with high morbidity, and of questionable effectiveness. It can lead to long term complications and suffering for the patient, often out of proportion to the original condition. The use of metal rods, screws and plates represent a rather crude approach to the treatment of discogenic pain. Despite its drawbacks, however, spinal fusion for discogenic pain remains common due to the lack of viable alternatives.
An alternative method that is not commonly used in practice but has been approved for use by the United States Food and Drug Administration (FDA), is the application of bone cerclage devices that can encircle the spinous processes or other vertebral elements and thereby create a restraint to motion. Physicians typically apply a tension or elongation to the devices that apply a constant and high force on the anatomy, thereby fixing the segment in one position and allowing effectively no motion. The lack of motion allowed after the application of such devices is thought useful to improve the likelihood of fusion performed concomitantly; if the fusion does not take, these devices can fail through breakage of the device or of the spinous process to which the device is attached. These devices are designed for static applications and are not designed to allow for a dynamic elastic resistance to flexion across a range of motion. The purpose of bone cerclage devices and the other techniques described above is to almost completely restrict measurable motion of the vertebral segment of interest. This loss of motion at a given segment gives rise to abnormal loading and motion at adjacent segments leading eventually to adjacent segment morbidity and other related problems.
The desperate need for better treatment options has lead to the introduction of a growing number of interspinous process devices. Designs vary from static spacers to dynamized devices. Furthermore, they are composed of a range of different materials including bone allograft, titanium, polyetheretherketone, and elastomeric compounds. The common link between them is the mechanical goal of distracting the spinous processes to affect the intervertebral relationship.
Recently, a minimally invasive and potentially more effective treatment for discogenic pain has been developed which offers a welcome alternative to the aforementioned conservative and invasive treatment extremes. A spinal implant (i.e. spinous process constraint) has been designed which inhibits spinal flexion while allowing substantially unrestricted spinal extension. Additional disclosure is provided in U.S. Patent Publication No. 2005/0216017A1 (now U.S. Pat. No. 7,458,981), the entire contents of which are incorporated herein by reference. Generally, the spinous process constraint is implanted with one or more tools that facilitate the procedure for a surgeon.
The successful placement of this innovative spinous process constraint is determined, in large part, by the way in which it is positioned in the patient. Additionally, during surgical implantation of a spinous process constraint, blood and tissue may make it difficult for a surgeon to see the implant. Accordingly, specific tools have been developed to make implant positioning and deployment faster, easier, less invasive, more accurate and more precise.
For the forgoing reasons, there is a need to provide methods and tools that facilitate deployment of spinous process constraints as well as other implants. As such, the following invention relates to methods and instruments for use in positioning and deploying a spinous process constraint like the implant described in U.S. Patent Publication No. 2005/0216017A1 (now U.S. Pat. No. 7,458,981).
2. Description of the Background Art
U.S. Patent Publication No. 2005/0216017A1 is described in greater detail below. Other patents and published applications that address problems associated with spinal stability include: U.S. Pat. Nos. 4,966,600; 5,011,494; 5,092,866; 5,116,340; 5,282,863; 5,395,374; 5,415,658; 5,415,661; 5,449,361; 5,456,722; 5,462,542; 5,496,318; 5,540,698; 5,609,634; 5,645,599; 5,725,582; 5,902,305; Re. 36,221; 5,928,232; 5,935,133; 5,964,769; 5,989,256; 6,053,921; 6,312,431; 6,364,883; 6,378,289; 6,391,030; 6,468,309; 6,436,099; 6,451,019; 6,582,433; 6,605,091; 6,626,944; 6,629,975; 6,652,527; 6,652,585; 6,656,185; 6,669,729; 6,682,533; 6,689,140; 6,712,819; 6,689,168; 6,695,852; 6,716,245; 6,761,720; 6,835,205; Published U.S. Patent Application Nos. 2002/0151978; 2004/0024458; 2004/0106995; 2004/0116927; 2004/0117017; 2004/0127989; 2004/0172132; 2005/0033435; 2005/0049708; 2006/0069447; Published PCT Application Nos. WO 01/28442 A1; WO 02/03882 A2; WO 02/051326 A1; WO 02/071960 A1; WO 03/045262 A1; WO 2004/052246 A1; WO 2004/073532 A1; and Published Foreign Application Nos. EP 0322334 A1; and FR 2 681 525 A1. However, each of these references suffers from one or more of the disadvantages previously described.